Blast-Resistant Glazing - ACS Symposium Series (ACS Publications)

Chapter 6

Blast-Resistant Glazing Gerald E. Meyers

Downloaded by UNIV OF NEW SOUTH WALES on January 11, 2018 | http://pubs.acs.org Publication Date: July 20, 1987 | doi: 10.1021/bk-1987-0345.ch006

Naval Civil Engineering Laboratory, Port Hueneme, CA 93043

Guidelines are presented for the design and evaluation of fixed or non-openable tempered glass windows to survive safely a prescribed blast environment described by a triangular-shaped pressure-time curve. These guidelines are in the form of load criteria for the design of both the glass panes and framing system for the window. The criteria account for both bending and membrane stresses and their effect on maximum principal stresses and the nonlinear flexural behavior of glass panes. H i s t o r i c a l r e c o r d s o f e x p l o s i o n e f f e c t s demonstrate t h a t b l a s t p r o p e l l e d g l a s s fragments from f a i l e d windows a r e o f t e n a major cause o f i n j u r i e s from e x p l o s i o n s . A l s o , f a i l e d window g l a z i n g o f t e n l e a d s t o a d d i t i o n a l i n j u r i e s as b l a s t p r e s s u r e can enter i n t e r i o r b u i l d i n g spaces and s u b j e c t p e r s o n n e l t o h i g h pressure j e t t i n g , incident overpressure, s e c o n d a r y d e b r i s impact and thrown body impact. These r i s k s a r e h e i g h t e n e d i n modern facilities, w h i c h o f t e n have l a r g e a r e a s o f g l a z i n g . T h i s paper p r e s e n t s g u i d e l i n e s f o r t h e d e s i g n , and e v a l u a t i o n , o f f i x e d o r non-openable windows t o s u r v i v e s a f e l y a p r e s c r i b e d b l a s t environment d e s c r i b e d by a t r i a n g u l a r - s h a p e d pressure-time curve. Window d e s i g n s u s i n g m o n o l i t h i c (unlaminated) thermally tempered g l a s s based on t h e s e g u i d e l i n e s c a n be e x p e c t e d t o p r o v i d e a p r o b a b i l i t y o f f a i l u r e e q u i v a l e n t t o t h a t p r o v i d e d by c u r r e n t s a f e t y s t a n d a r d s f o r s a f e l y r e s i s t i n g wind l o a d s . The g u i d e l i n e s a r e p r e s e n t e d i n t h e form o f l o a d c r i t e r i a f o r t h e d e s i g n o f b o t h t h e g l a s s panes and f r a m i n g system f o r t h e window. The c r i t e r i a account f o r both bending and membrane s t r e s s e s and t h e i r e f f e c t on maximum p r i n c i p a l s t r e s s e s and t h e n o n l i n e a r b e h a v i o r o f g l a s s panes. F u r t h e r r e s e a r c h i s underway t o extend t h i s d e s i g n c r i t e r i a t o b o t h l a m i n a t e d tempered g l a s s and polycarbonate.

This chapter not subject to U.S. copyright Published 1987 American Chemical Society

Scott and Doemeny; Design Considerations for Toxic Chemical and Explosives Facilities ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

108

TOXIC CHEMICAL AND EXPLOSIVES FACILITIES


Background The design c r i t e r i a for blast resistant glazing covers monolithic thermally tempered glass meeting the requirements of Federal Specifications DD-G-1403B and DD-G-451d. Additionally, thermally tempered glass i s required to meet the minimum fragment weight requirements of ANSI Z97.1-1984. Annealed glass i s the most common form of glass available today. Depending upon manufacturing techniques, i t i s also known as plate, f l o a t or sheet glass. During manufacture, i t i s cooled slowly. The process results i n very l i t t l e , i f any, residual compressive surface stress. Consequently, annealed glass i s of r e l a t i v e l y low strength when compared to tempered glass. Furthermore, i t has large variations i n strength and fractures into dagger-shaped, razor-sharp fragments. For these reasons, annealed glass i s not recommended for use i n b l a s t - r e s i s t a n t windows. Thermally tempered glass i s the most r e a d i l y available tempered glass on the market. It i s manufactured from annealed glass by heating to a high uniform temperature and then applying cont r o l l e d , rapid cooling. As the internal temperature p r o f i l e relaxes towards uniformity, i n t e r n a l stresses are created. The outer layers, which cool and contract f i r s t , are set i n compression, while i n t e r n a l layers are set i n tension. As i t i s rare for flaws, which act as stress magnifiers, to exist i n the i n t e r i o r of tempered glass sheets, the internal t e n s i l e stress i s of r e l a t i v e l y minimal consequence. As f a i l u r e originates from t e n s i l e stresses exciting surface flaws i n the glass, precompression permits a larger load to be c a r r i e d before the net t e n s i l e strength of the tempered glass pane i s exceeded. Thermally tempered glass i s t y p i c a l l y four to f i v e times stronger than annealed glass. The fracture c h a r a c t e r i s t i c s of tempered glass are superior to those of annealed glass. Due to the high s t r a i n energy stored by the prestress, tempered glass w i l l eventually fracture into small cube-shaped fragments instead of the razor-sharp, dagger-shaped fragments associated annealed glass. Breakage patterns of side and rear windows i n American automobiles are a good example of the f a i l u r e mode of thermally or heat-treated tempered glass. Semi-tempered glass i s often marketed as safety or heattreated glass. However, i t exhibits neither the d i c i n g characteri s t i c upon breakage nor the higher t e n s i l e strength associated with f u l l y tempered glass. Semi-tempered glass i s not recommended for b l a s t - r e s i s t a n t windows. Another common glazing material i s wire-reinforced glass, annealed glass with an embedded layer of wire mesh. Its only use i s as a f i r e - r e s i s t a n t b a r r i e r . Wire glass has the fracture and low strength c h a r a c t e r i s t i c s of annealed glass and, although the wire binds fragments, i t contributes metal fragments as an addit i o n a l hazard. Wire glass i s never recommended for b l a s t - r e s i s t a n t windows. Design C r i t e r i a for Glazing Specified Glazing. The design of b l a s t - r e s i s t a n t windows i s currently r e s t r i c t e d to heat-treated, fully-tempered glass i n fixed



6.

MEYERS

Blast-Resistant Glazing

109

or non-openable frames meeting both Federal Specification DD-G-1403B and ANSI Z97.1-1984. To preclude the p o s s i b i l i t y that stress concentrations at tong marks w i l l cause premature f a i l u r e s , the glass must be tempered horizontally or i n a basket. No nicks or imperfections about the edges should be permitted. Although thermally tempered glass exhibits the safest f a i l u r e mode of any glass, f a i l u r e under blast loading s t i l l presents a s i g n i f i c a n t health hazard. Results from blast tests reveal that upon fracture, tempered glass fragments may be propelled i n cohesive clumps that only fragment upon impact into smaller rock-salt-shaped fragments. Even i f the tempered glass breaks up i n i t i a l l y into small frag ments, s u f f i c i e n t blast pressure can propel the fragments at a high enough v e l o c i t y to constitute a severe danger. Because of the high l i k e l i h o o d of multiple edge and corner impacts by fragments of tempered glass, biomedical experts warn that the 58-ft-lb c r i t e r i o n for acceptable fragments should not be applied to glass. Because of these fragment dangers, b l a s t - r e s i s t a n t glazing should be designed to survive with high p r o b a b i l i t y i t s design threat. Design Charts. Charts are presented i n Figures 1 through 12 for both the design and evaluation of glazing to survive safely a prescribed blast loading with a p r o b a b i l i t y of f a i l u r e no greater than 0.001. The charts relate the peak blast overpressure capac i t y , B, of thermally tempered glazing to a l l combinations of the following design parameters: length/width r a t i o = 1.00, 1.50, 2.00, and 4.00; 1.00 £ glass area £ 25 f t ; 12 < width < 60 inches; 2 £ blast duration £ 1,000 msec; and thickness = 1/4, 5/16, 3/8, 1/2, 5/8, and 3/4 inch (nominal). Thermally tempered glass up to 3/4 inch thick can be e a s i l y purchased i n the united States. Thicknesses greater than 3/4 inch can only be obtained by lamina tion. Research and blast load testing are required to develop design curves with confidence for laminated glass. Each chart has a series of curves. Each curve corresponds to the pane dimension shown to the right of the curve. Adjacent to the pane dimension i s the value of Β (peak blast overpressure capacity) corresponding to Τ = 1,000 msec. The posted value of Β i s intended to reduce errors when interpolating between curves. 2

Required Design C r i t e r i a for Frame Sealants, Gaskets, and Beads. A l l gaskets or beads are required to be at least 3/8 inch wide with a Shore "A" durometer hardness of 50 and conform to ASTM Specification C509-84 ( C e l l u l a r Elastomeric Preformed Gasket and Sealing Material). The bead and sealant are required to form a weatherproof seal. Glazing Setting. Minimum frame edge clearances, face clearance, and b i t e ( i l l u s t r a t e d i n Figure 13) are s p e c i f i e d i n Table I. Frame Loads. The window frame must develop the s t a t i c design strength of the glass pane, r , given i n Table I I . Otherwise, the design i s inconsistent with frame assumptions, and the peak blast pressure capacity of the window assemblies w i l l produce a f a i l u r e rate i n excess of the prescribed f a i l u r e rate. This results


110


100-, a/b t


a*.

-

1.00 1/4 in

W W I I 24x24 30x30 36x36 42x42 48x48 54x54 60x60

too

b χ a (in.)

B(psi)

12 χ 12

16.8

18 x 1 8

7.60

24x24

5.16

30x30

3.45

36x36

2A5

42x42

1.83

48x48

D u r a t i o n of B l a s t

Pressure,

Τ

1.43

54x54

1.14

60x60

0.94

(msec)

Figure 1. Peak blast pressure capacity f o r tempered glass panes: a/b = 1.00, t = 1/4 and 5/16 i n .


6.

MEYERS


111


b χ a (in.)

1.00 t • 1/2 in.

B(psJ)

12x12

25.1

18x18

11.1

24x24

6.48

30x30

5.12

36x36

3.55

42x42

2.63

48x48

106

54x54

1.66

60x60

136

a/D -

bxaUn.)

Β

(DM)

12x12

43.9

18x18

195

24x24

10.9

30x30

7.10

36x36 42x42

4.58

48x48

3Λ8

54x54

2.77

60x60

230

5.43

to 100 D u r a t i o n of B l a s t P r e s s u r e , Τ ( m s e c )

Figure 2. Peak b l a s t pressure capacity f o r tempered glass panes: a/b = 1.00, t = 3/8 and 1/2 i n .


112



i-l ι

'

1

1 M MM 1 1 I I I I IU 1 1 I to too D u r a t i o n of B l a s t P r e s s u r e , Τ ( m s e c )

M i l l } 1000





MEYERS




114




MEYERS

Blast-Resistant Gfozing


b χ a (in.)

B(psi)

12x18

41.9

18x27

18.6

24x36

105

30x45

6.72

36x54

4.74

42x63 48x72

3.77 3.19

10 too D u r a M o n of B l a s t P r e s s u r e , Τ ( m s e c )





116




MEYERS


Figure 8. Peak b l a s t pressure capacity f o r tempered glass panes a/b = 2.00, t = 3/8 and 1/2 i n .




D u r a t i o n of B l a s t P r e s s u r e , Τ

(msec)

Figure 9. Peak blast pressure capacity f o r tempered glass panes: a/b =2.00, t = 5/8 and 3/4 i n .


MEYERS

119



6.

F i g u r e 10. a/b = 4.00,

Peak b l a s t p r e s s u r e c a p a c i t y f o r tempered g l a s s t = 1/4 and 5/16 i n .

panes:




120

Figure 11. Peak blast pressure capacity for tempered glass panes: a/b = 4.00, t = 3/8 and 1/2 i n .




MEYERS

F i g u r e 12. Peak b l a s t p r e s s u r e c a p a c i t y f o r tempered g l a s s panes a/b = 4.00, t = 5/8 and 3/4 i n .


122



A - edge clearance Β - bite C - face clearance

Figure 13.

Edge, face, and b i t e requirements.


6.

123


MEYERS

because frame deflections induce higher p r i n c i p a l t e n s i l e stresses in the pane, thus reducing the capacity available to safely r e s i s t the blast loading. Table I. Minimum Design Thicknesses, Clearances and Bite Requirements


Glass Thickness (Nominal) in

mm

Actual Glass Thickness f o r Design, t (in)

5/32 3/16 1/4 3/8 1/2 5/8 3/4

4.0 5.0 6.0 10.0 12.0 16.0 19.0

0.149 0.180 0.219 0.355 0.469 0.594 0.719

"c"

"A" Minimum Edge Clearance (in)

"B" Nominal Bite (in)

Minimum Face Clearance (in)

3/16 3/16 1/4 5/16 3/8 3/8 3/8

1/2 1/2 1/2 1/2 1/2 1/2 1/2

1/8 1/8 1/8 3/16 1/4 1/4 5/16

In addition to the load transferred to the frame by the glass, frame members must also r e s i s t the s t a t i c design load, r , applied to a l l exposed members. Maximum allowable limits f o r frame design are: 1.

Deflection: No frame member should have a r e l a t i v e displacement exceeding l/264th of i t s span or 1/8 inch, whichever i s less.

2.

Stress: The maximum stress i n any member should not exceed f /1.65, where f = y i e l d stress of the members material. y

y

3.

Fasteners : The maximum stress i n any fastener should not exceed f /2.00. y The design loads for the glazing are based on large deflection plate theory, but the resulting transferred design loads f o r the frame are based on an approximate solution of small d e f l e c t i o n theory f o r normally loaded plates. Analysis indicates this approach to be considerably simpler and more conservative than using the frame loading based exclusively on large deflection plate behavior, c h a r a c t e r i s t i c of window panes. The effect of the s t a t i c design load, r , applied d i r e c t l y to the exposed frame members of width, w, i s aiso considered. The design load, r , produces a l i n e shear, ν , applied by the long side, a, of the pane equal to: χ

V

X

=

C r b s i n (πχ/a) + r w, l b / i n x u ' ' u * '

(1)

The design load, r , produces a l i n e shear, V , applied by the short side, b, of the pane equal to: y


124

TOXIC CHEMICAL A N D EXPLOSIVES

Table I I .

FACILITIES

S t a t i c Design Strength, r ^ C p s i ) , f o r Tempered Glass* long dimension of glass pane (In.); b - short dimension of glass pane (ln.)j


ASPECT RATIO - 1.00 Glass

Static Design Strength (psl) for a Window thickness, t, of -·

b χ a (in.)

3/4 in.

5/8 in.

1/2 in.

3/8 in.

12x12 13x13 14x14 15x15 16x16 17x17 18x18 19x19 20x20 21x21 22x22 23x23 24x24 25x25 26x26 27x27 28x28 29x29 30x30 31x31 32x32 33x33 34x34 35x35 36x36 37x37 38x38 39x39 40x40 41x41 42x42 43x43 44x44 45x45 46x46 47x47 48x48 49x49 50x50 51x51 52*52 53x52 54x54 55x55 56x56 57x57 58x58 59x59 60x60

206 176 151 132 116 103 91.6 82.2 74.2 67.3 61.3 56.1 51.5 47.5 43.9 40.7 37.9 35.3 33.0 30.9 29.0 27.4 26.0 24.8 23.6 22.5 21.5

141 120 103 90.1 79.2 70.1 62.5 56.1 50.7 46.0 41.9 38.3 35.2 32.4 30.0 27.9 26.2 24.6 23.2 21.9 20.8 19.7 18.7 17.8 17.0 16.2 15.4 14.8 14.4 14.1 13.8 13.5 13.2 13.0 12.9 12.8 12.7 12.6 12.6 12.4 11.9 11.5 11.1 10.7 10.3 9.99 9.66 9.38 9.11

87.7 74.7 64.5 56.1 49.3 43.7 39.0 35.0 31.6 28.6 26.4 24.4 22.7

50.3 42.8 36.9 32.2 28.3 25.5 23.1 21.0 19.1 17.7 16.3 15.1 14.3 13.8 13.4 12.9 12.8 12.6 12.6 12.0 11.3 10.6 10.0 9.50 9.05 8.63 8.24. 7.88 7.57 7.30 7.04 6.80 6.56 6.32 6.08 5.86 5.65 5.45 5.27 5.09 4.92 4.76 4.61 4.47 4.33 4.20 4.08 3.97 3.85

50.5

19.7 18.8 18.1 17.3 16.7 16.0 15.4 14.9 14.5 14.2 14.0 13.7 13.5 13.3 13.1 12.9 12.8 12.7 12.7 12.6 12.6

Î1-2 11! J

18.5 17.4 16.4 15.4 14.6 14.2 13.8 13.5 13.2 12.8 12.7 12.7 12.6 12.5 11.9 11.4 10.9 10.4 9.99 9.59 9.24 8.91 8.59 8.30 8.02 7.76 7.54 7.33 7.13 6.94 6.76 6.59 6.40 6.22

5/16 in. 27.5 23.9 21.1 18.7 16.7 15.1 14.1 13.5 12.9 12.7 12.6 11.8 10.9 10.1 9.39 8.80 8.26 7.78 7.39 7.04 6.71 6.39 6.07 5.77 5.50 5.24 5.01 4.79 4.58 4.39 4.21 4.05 3.90 3.75 3.62 3.49 3.37 3.25 3.15 3.04 2.95 2.85 2.77 2.68 2.60 2.53 2.45 2.38 2.32

1/4 in. 20.2 17.6 15.5 14.2 13.4 12.7 12.6 12.1 11.0 10.0 9.20 8.52 7.91 7.43 7.00 6.62 6.22 5.86 5.53 5.22 4.94 4.69 4.45 4.23 4.04 3.86 3.69 3.53 3.39 3.25 3.12 3.00 2.89 2.78 2.68 2.58 2.49 2.41 2.33 2.25 2.18 2.11 2.05 1.99 1.93 1.87 1.82 1.77 1.72

•Panes to the right and below the stepped dividing line behave according to large deflection plate theory.


MEYERS


Table II. Continued.

(a · long dimension of glass pane (in.); b · short dimension of glass pane (in.)]


ASPECT RATIO - 1.50 Glass Size, b χ a (in.) 12x18 13x19.5 14x21 15x22.5 16x24 17x25.5 18x27 19x28.5 20x30 21x31.5 22x33 23x34.5 24x36 25x37.5 26x39 27x40.5 28x42 29x43.5 30x45 31x46.5 32x48 33x49.5 34x51 35x52.5 36x54 37x55.5 38x57 39x58.5 40x60 41x61.5 42x63 43x64.5 44x66 45x67.5 46x69 47x70.5 48x72

Static Design Strength (psi) for a Window Thickness t t, of - 3/4 in.

5/8 in.

123 105 90.2 78.6 69.1 61.2 54.6 49.0 44.2 40.1 36.5 33.4 30.7 28.3 26.2 24.3 22.6 21.0 19.7 18.4 17.3 16.2 15.3 14.4 13.6 13.0 12.5 12.0 11.6 11.2 10.8 10.4 10.1 9.71 9.42 9.25 9.08

83.8 71.4 61.6 53.6 47.2 41.8 37.3 33.4 30.2 27.4 24.9 22.8 21.0 19.3 17.9 16.6 15.4 14.4 13.4 12.8 12.2 11.6 11.1 10.6 10.2 9.78 9.42 9.21 9.01 8.82 8.60 8.35 8.12 7.90 7.69 7.62 7.55

1/2 in.

3/8 in.

52.3 44.5 38.4 33.4 29.4 26.0 23.2 20.8 18.8 17.1 15.6 14.2 13.1 12.4 11.7 11.0 10.4 9.89 9.42 9.1Î 8.91 8.65 8.34 8.05 8.02 7.99 7.96 7.93 7.91 7.88 7.85 7.77 7.69 7.62 7.35 7.06 6.78

29.9 25.5 22.0 19.2 16.8 14.9 13.3 12.3 11.4 10.6 9.86 9.32 8.98 8.64 8.24 7.86 7.85 7.85 7.84 7.83 7.82 7.72 7.62 7.28 6.90 6.55 6.22 5.92 5.64 5.38 5.13 4.91 4.70 4.50 4.31 4.14 3.97

5/16 in.

1/4 in.

16.3 13.9 12.3 11.1 10.0 9.31 8.85 8.84 7.83 7.81 7.80 7.77 7.77 7.63 7.19 6.69 6.24 5.83 5.47 5.13 4.83 4.55 4.30 4.07 3.85 3.66 3.47 3.33 3.21 3.09 2.98 2.88 2.77 2.66 2.56 2.47 2.38

11.9 10.5 9.43 ô.êô 8.26 8.14 8.02 7.90 7.78 7.62 7.03 6.45 5.95 5.50 5.10 4.74 4.42 4.14 3.88 3.64 3.43 3.27 3.13 3.00 2.87 2.74 2.61 2.50 2.39 2.29 2.19 2.10 2.02 1.94 1.86 1.79 1.73

•Panes to the right and below the stepped dividing line behave according to large deflection plate theory.

Continued on next page.



Table II. Continued. [a - long dimension of glass pane ( i n . ) ; b - short dimension of glass pane ( i n . ) ] ASPECT RATIO - 2.00


Glass Size, b χ a (in.) 12x24 13x26 14x28 15x30 16x32 17x34 18x36 19x38 20x40 21x42 22x44 23x46 24x48 25x50 26x52 27x54 28x56 29x58 30x60 31x62 32x64 33x66 34x68 35x70 36x72 37x74 38x76 39x78 40x80 41x82 42x84

S t a t i c Design Strength ( p s i ) f o ra Window Thickness, t:, of 3/4 i n . 97.6 83.1 71.7 62.4 54.9 48.6 43.4 38.9 35.1 31.9 29.0 26.6 24.4 22.5 20.8 19.3 17.9 16.7 15.6 14.6 13.7 12.9 12.2 11.5 10.8 10.3 9.73 9.24 8.78 8.37 8.03

5/8 i n .

1/2 i n .

3/8 i n .

5/16 i n .

1/4 i n .

66.6 56.7 48.9 42.6 37.5 33.2 29.6 26.6 24.0 21.7 19.8 18.1 16.6 15.3 14.2 13.2 12.2 11.4 10.7 9.98 9.36 8.80 8.31 7.91 7.53 7.18 6.86 6.62 6.42 6.23 6.05

41.5 35.4 30.5 26.6 23.4 20.7 18.5 16.6 14.9 13.6 12.4 11.3 10.4 9.56 8.84 8.23 7.73 7.27 6.86 6.57 6.32 6.08 5.87 5.66 5.47 5.29 5.12 4.96 4.81 4.67 4.60

23.8 20.3 17.5 15.2 13.3 11.9 10.6 9.49 8.56 7.85 7.25 6.73 6.39 6.08 5.79

13.0 11.0 9.52 8.31 7.43 6172 6.26 5.86 5.51 5.19 4. 4.64 4.55 4.47 4.40 4.39 4.38 4.37 4.31 4.25 4.08 3.85 3.64 3.44 3.26 3.11 2.97 2.84 2.72 2.60 2.50

9.05 7.81 6.87 6.29 5.81 5l4Ô 5.03 4.71 4.56 4.46 4.42 4.39 4.37 4.32 4.24 4.01 3.74 3.50 3.28 3.09 2.93 2.78 2.64 2.51 2.39 2.28 2.18 2.08 1.98 1.89 1.80

5.53 5.29 5.07 4.86 4.67 4.58 4.52 4.47 4.41 4.40 4.39 4.38 4.37 4.34 4.30 4.25

So

ASPECT RATIO - 4.00 Glass Size, b χ a (in.) 12x48 13x52 14x56 15x60 16x64 17x68 18x72 19x76 20x80 21x84 22x88 23x92 24x96 25x100 26x104 27x108 28x112 29x116 30x120

S t a t i c Design Strength ( p s l ) f o r a Window Thickness, t , of — 3/4 i n . 75.7 64.5 55.6 48.5 42.6 37.7 33.7 30.2 27.3 24.7 22.5 20.6 18.9 17.5 16.1 15.0 13.9 13.0 12.1

5/8 In. 51.7 44.0 38.0 33.1 29.1 25.8 23.0 20.6 18.6 16.9 15.4 14.1 12.9 11.9 11.0 10.2 9.49 8.85 8.27

1/2 In.

3/8 In.

5/16 i n .

32.2 27.5 23.7 20.6 18.1 16.1 14.3 12.9 11.6 10.5 9.59 8.77 8.05 7.42 6.86 6.36 5.92 5.52 5.15

18.5 15.7 13.6 11.8 10.4 9.20 8.20 7.36 6.65 6.03 5.49 5.03 4.63 4.28 3.97 3.70 3.45 3.22 3.02

10.1 8.57 7.39 6.43 5.66 5.01 4.49 4.05 3.67 3.34 3.06 2.81 2.59 2.39 2.23 2.09 1.96 1.84 1.75

1/4 i n . 7.02 5.99 5.16 4.52 3.99 3.56 3.19 2.87 2.60 2.37 2.18 2.02 > 1.88 1.76 1.66 1.57 1.49 1.41 1.34

•Panes to the r i g h t and below the stepped d i v i d i n g l i n e behave according to large d e f l e c t i o n p l a t e theory.


6.


MEYERS

V

y

=

c

r

b

y

s

i

n

u

Ciry/b) + r

127 u

w, l b / i n

(2)

The design load, r , also produces a corner concentrated load, R, tending to u p l i f t corners of the window pane equal to: R

=

2

C r b , lb κ u

(3)

D

D i s t r i b u t i o n of these forces as loads acting on the window frame i s shown i n Figure 14. Table III presents the design c o e f f i c i e n t s , C , C , and C f o r p r a c t i c a l aspect ratios of the window pane. LÎnear interpofation can be used for aspect ratios not presented.


R

7

Table I I I .

a/b 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90 2.00 3.00 4.00

C

Coefficients f o r Frame Loading

R

0.065 0.070 0.074 0.079 0.083 0.085 0.086 0.088 0.090 0.091 0.092 0.093 0.094

C X

0.495 0.516 0.535 0.554 0.570 0.581 0.590 0.600 0.609 0.616 0.623 0.644 0.687

C y

0.495 0.516 0.533 0.551 0.562 0.574 0.583 0.591 0.600 0.607 0.614 0.655 0.685

Although frames with mullions are included i n the design c r i t e r i a , i t i s recommended that single pane frames be used. Experience indicates that mullions complicate the design and reduce r e l i a b l e fabrication of blast-resistant frames. I f mullions are used, the loads given by Equations 1, 2, and 3 should be used to check the frame mullions and fasteners for compliance with the deflection and stress c r i t e r i a stated above. Special design consideration should be taken so that the deflection of the building wall w i l l not impose deflections on the frame greater than l/264th of the length of the edge of the pane. Where i t i s impossible to achieve enough building wall r i g i d i t y , i t is recommended that the frames be pinned at the corners to the structure i n a manner to i s o l a t e the frame from wall rotation. Rebound. Response to the dynamic blast load, w i l l cause the window to rebound with a negative (outward) deflection. The outward pane displacement and the stresses produced by the negative deflection must be safely resisted by the window while p o s i t i v e pressures act on the window. Otherwise, the window which safely r e s i s t s stresses



TOXIC CHEMICAL A N D EXPLOSIVES

FACILITIES

Figure 14. D i s t r i b u t i o n of l a t e r a l load transmitted by glass pane to the window frame.



6.

MEYERS


129

induced by p o s i t i v e (inward) displacements may f a i l i n rebound while the p o s i t i v e pressure s t i l l acts. This can propel glass fragments i n t o the i n t e r i o r of the structure. However, i f the window f a i l s i n rebound during the negative (suction) phase of the b l a s t loading, glass fragments w i l l be drawn away from the struc ture. I f glass f a i l u r e does not present a hazard t o personnel outside the structure, glass may be permitted t o f a i l during the negative load phase. Rebound w i l l occur during the negative load phase i f the e f f e c t i v e b l a s t duration, T, i s no greater than one h a l f the natural period of v i b r a t i o n , Τ , of the glass pane. For Τ > 10 Τ , s i g n i f i c a n t rebound does not occur during the p o s i t i v e b l a s t pressure phase. Therefore, rebound can be neglected as a design consideration. For 0.5 < T/T < 10, the frame must be designed for the peak negative resistance occurring during the p o s i t i v e overpressure phase. I n s t a l l a t i o n Inspection A survey of glazing f a i l u r e s due t o wind load indicates that improper i n s t a l l a t i o n of s e t t i n g blocks, gaskets or l a t e r a l shims, or poor edge b i t e i s a s i g n i f i c a n t cause of f a i l u r e because of the resultant unconservative support conditions. To prevent premature glass f a i l u r e , a strenuous q u a l i t y control program i s required.

Literature Cited Meyers, G.E. Design Criteria and Test Acceptance Specification for Blast Resistant Windows, Department of Defense Explosive Safety Seminar, Anaheim, CA, Aug 1986. RECEIVED May 13, 1987


Blast-Resistant Glazing - ACS Symposium Series (ACS Publications)

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